Hammer drills are employed to do a task of, e.g., drilling a concrete structures. There arises such an instance that a screw is tightened to an anchor embedded into a hole formed by the drilling work. However, typical hammer drills are always accompanied by striking motion and therefore cannot be used in tightening the screw, which requires the additional use of an electric driver.
Also known in the art is a hammer drill of the type capable of releasing a striking motion and transmitting only a rotation force to an output bit. This type of hammer drill has no ability to tighten the screw with a suitable torque but tends to, not infrequently, tighten the screw too heavily.
In the meantime, Japanese Patent Laid-open Publication Nos. 2000-233306 and H7-1355 disclose a vibratory drill and an impact drill wherein a vibratory load or an impact load can be released and a tightening torque can be controlled using a tightening-torque adjusting clutch. However, no tightening-torque adjusting clutch has heretofore been employed in the hammer drills in which an axial striking force is applied against a rotatingly driven output bit through the use of an axially reciprocating striker. For this reason, the conventional hammer drills still require the use of an electric driver to perform the task of tightening a screw as noted above.